JP2007194048A - Ion-conducting binder, membrane-electrode assembly and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ion-conducting binder which is economical, environment-friendly, superior in moldability, and oxidation stability; and to utilize it. <P>SOLUTION: The ion-conducting binder is used for a membrane-electrode assembly for a polymer electrolyte fuel cell comprising a polymer electrolyte membrane, and two gas diffusion electrodes jointed to the electrolyte membrane by sandwiching the membrane, and contains, as components, a polymer block (A) using an aromatic vinyl-based compound unit where α-carbon is quarternary carbon as a main repeating unit, and a flexible polymer block (B). In the ion-conducting binder, the polymer block (A) has a monovalent anion-conducting group, multivalent anion-conducting groups are bound to one another in a form cross-linking the polymer blocks (A) to one another, and/or the multivalent anion-conducting groups are bound to one another in a form cross-linking the aromatic vinyl-based compound units to one another in the polymer block (A). Its solution or suspension, this membrane-electrode assembly and this polymer electrolyte fuel cell are also provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ion conductive binder used in a membrane-electrode assembly constituting a solid polymer fuel cell, a membrane-electrode assembly using the ion conductive binder, and the membrane-electrode assembly. The present invention relates to a polymer electrolyte fuel cell.

  In recent years, fuel cells have attracted attention as a clean power generation system that is friendly to the global environment. Fuel cells are classified into phosphoric acid type, molten carbonate type, solid oxide type, solid polymer type, etc., depending on the type of electrolyte. Among these, polymer electrolyte fuel cells are applicable to electric vehicle power supplies, portable equipment power supplies, and household cogeneration systems that use both electricity and heat from the viewpoints of low-temperature operability, small size, and light weight. It is being considered.

  A polymer electrolyte fuel cell is generally configured as follows. First, on both sides of an electrolyte membrane having proton conductivity, a catalyst layer containing carbon powder carrying a white metal catalyst and an ion conductive binder (ion is usually proton) made of a polymer electrolyte is formed. A gas diffusion layer, which is a porous material through which fuel gas and oxidant gas are passed, is formed outside each catalyst layer. Carbon paper, carbon cloth, or the like is used as the gas diffusion layer. A structure in which the catalyst layer and the gas diffusion layer are integrated is called a gas diffusion electrode, and a structure in which a pair of gas diffusion electrodes is bonded to the electrolyte membrane so that the catalyst layer faces the electrolyte membrane is a membrane-electrode assembly ( MEA (Mebrane Electrode Assembly). On both sides of this membrane-electrode assembly, separators having electrical conductivity and airtightness are disposed. A gas flow path for supplying a fuel gas or an oxidant gas (for example, air) to the electrode surface is formed in a contact portion of the membrane-electrode assembly and the separator or in the separator. Electric power is generated by supplying a fuel gas such as hydrogen or methanol to one electrode (fuel electrode) and an oxidant gas containing oxygen such as air to the other electrode (oxygen electrode). That is, at the fuel electrode, the fuel is ionized to produce protons and electrons, the protons pass through the electrolyte membrane, the electrons travel through an external electric circuit formed by connecting both electrodes, and are sent to the oxygen electrode, Water is produced by the reaction. In this way, the chemical energy of the fuel can be directly converted into electric energy and taken out.

  For such a proton exchange type fuel cell, an anion exchange type fuel cell using an anion conductive membrane and an anion conductive binder (anion is usually a hydroxide ion) has been studied. An anion exchange fuel cell is known to reduce overvoltage at the oxygen electrode, and is expected to improve energy efficiency. In addition, when methanol is used as the fuel, it is said that methanol crossover in which methanol permeates the electrolyte membrane between the electrodes is reduced. The structure of the polymer electrolyte fuel cell in this case is basically the same as that of the proton exchange type fuel cell except that an anion conductive membrane and an anion conductive binder are used instead of the proton conductive membrane and the proton conductive binder. Similarly, the mechanism of electric energy generation is that oxygen, water, and electrons react at the oxygen electrode to generate hydroxide ions, and the hydroxide ions react with hydrogen at the fuel electrode through the anion conductive membrane. Thus, water and electrons are generated, and the electrons move through an external electric circuit formed by connecting both electrodes and are sent to the oxygen electrode, and react with oxygen and water again to generate hydroxide ions. In this way, the chemical energy of the fuel can be directly converted into electric energy and taken out.

  In the proton exchange type fuel cell and the anion exchange type fuel cell, the electrode reaction is carried out using the catalyst layer as a reaction site, the catalyst surface, the fuel gas or the oxidant gas, and the three-phase interface of the ion conductive binder as the polymer electrolyte. Happens at. The ion conductive binder is used for the purpose of binding the catalyst and increasing the utilization efficiency of the catalyst through the transfer of protons or hydroxide ions from the catalyst layer to the electrolyte membrane. Therefore, it is difficult for a catalyst not coated with an ion conductive binder to contribute to the reaction because it cannot form a three-phase interface, and to obtain high efficiency, a fuel gas or an oxidant gas is diffused. Therefore, a precise structure design of the catalyst layer such as a pore structure for the catalyst and a dispersed state of the catalyst is important. In addition, in the gas diffusion electrode part, the catalyst surface is covered with water contained in the reaction gas or water generated at the oxygen electrode, and the fuel gas or oxidant gas cannot contact the catalyst surface and power generation stops. In some cases, the electrode reaction may be stopped by preventing the supply or discharge of the fuel gas or the oxidant gas. Therefore, the water repellency of the gas diffusion electrode part is required.

  As for joining of the gas diffusion electrode and the electrolyte membrane, a method of joining by hot pressing or the like is known. However, since it is difficult to obtain good bonding strength and electrical bonding state simply by hot pressing, an ion conductive binder is applied as an adhesive resin to the catalyst layer surface of the gas diffusion electrode, and the gas diffusion electrode and It is preferable to improve the adhesion of the electrolyte membrane. For such applications, ion conductive binders are generally used in solution.

  As an ion conductive binder used in the proton exchange fuel cell, Nafion (perfluorosulfonic acid polymer as described in Patent Document 1 and Patent Document 2) is used because it is chemically stable. Nafion, a registered trademark of DuPont, the same applies hereinafter). However, since Nafion is a fluorine-based polymer, it is very expensive. In addition, the fluorine-containing polymer contains fluorine, and environmental considerations are required during synthesis and disposal.

  Because of these problems, ion-conductive binders have been developed to replace fluorine-based polymers. For example, aromatic engineering plastic resins into which ion-conducting groups such as sulfonic acid groups are introduced have been studied, but many of them have a high affinity with water. In such ion-conducting binders, the binder itself generates power. The moisture contained in the reaction gas contained therein and the water generated from the oxygen electrode gradually elute out of the battery system, and the electrode deteriorates and cannot ensure sufficient operation time. Although it is possible to make it insoluble in water by reducing the amount of ion-conducting groups introduced, high output cannot be obtained because sufficient ion conductivity is not exhibited. In addition, a resin that has been insoluble in water by introducing a crosslinking group has been studied, but since it is insoluble in organic solvents, it must be suspended in an appropriate solvent and used in the catalyst layer. However, it is difficult to form an effective three-phase interface.

  In addition to aromatic engineering plastic resins, ion conductive binders made of styrene thermoplastic elastomers have been proposed (Patent Document 3 and Patent Document 4). For example, a sulfonated product of SEBS (polystyrene-poly (ethylene-butylene) -polystyrene triblock copolymer) has been proposed, which is hardly soluble in water and has a good bonding strength with an electrolyte membrane. It is disclosed. However, in general, in an ion conductive binder used for an electrode catalyst layer constituting a solid polymer fuel cell, a polymer skeleton is formed by hydrogen peroxide generated by a side reaction of an electrode reaction or a hydroxyl radical derived from hydrogen peroxide. Decrease in ion conductivity due to decomposition and elution of the ion conductive binder itself out of the battery system are observed. Since SEBS has structurally unstable tertiary carbon, it is considered that chemical stability, particularly oxidation stability, is insufficient. As a result of our experiments, it became clear that the oxidation stability was insufficient. This means that the operable time is limited because the deterioration of the ion conductive binder proceeds during power generation.

On the other hand, as an anion conductive binder used in an anion exchange type fuel cell, one obtained by converting a sulfonic acid group of a perfluorosulfonic acid polymer into an anion exchange group is known. For example, in Patent Document 5, tetrafluoroethylene and CF ₂ ═CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₃ F are copolymerized and then N, N, N′-trimethylethylenediamine is allowed to act. Is disclosed (paragraph 0026). However, this ion conductive binder has the same drawbacks as Nafion. Further, Patent Document 6 discloses an anion exchange resin obtained by aminating a chloromethylated copolymer of an aromatic polyethersulfone and an aromatic polythioethersulfone as an anion conductive binder (paragraph 0046). However, this ion conductive binder has a high affinity with water and has the same drawbacks as the above-described aromatic engineering plastic cation conductive binder. Further, Patent Document 7 discloses an anion conductive binder comprising a quaternary ammonium group introduced into a polystyrene-poly (ethylene-butylene) -polystyrene triblock copolymer or the like as an anion conductive binder (paragraph). 0041 and 0045). However, this anion conductive binder has the same disadvantages as the above cation conductive binder having a similar skeleton.

As described above, an anion conductive binder that is economical, does not contain fluorine, and has excellent oxidation stability has not been proposed.
Japanese Patent Publication No.2-7398 JP-A-3-208260 JP 2002-164055 A Special Table 2000-513484 JP 2000-331693 A Japanese Patent Laid-Open No. 11-273695 JP 2002-367626 A

  The present invention provides an ion conductive binder that is economical, environmentally friendly, excellent in moldability, and excellent in oxidation stability and consequently durability, a membrane-electrode assembly using the ion conductive binder, and the An object of the present invention is to provide a polymer electrolyte fuel cell using a membrane-electrode assembly.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a polymer block (A) having a repeating unit of an aromatic vinyl compound whose α-carbon is a quaternary carbon and a flexible polymer The present invention has found that a block copolymer having a block (B) as a constituent component and an anion conductive group bonded to the polymer block (A) is excellent in moldability and oxidation stability as an ion conductive binder. Was completed.

  That is, the present invention provides a membrane-electrode assembly for a polymer electrolyte fuel cell comprising a polymer electrolyte membrane and two gas diffusion electrodes joined to the polymer electrolyte membrane with the membrane interposed therebetween. An ion conductive binder to be used, the polymer block (A) and the flexible polymer block (B) having an aromatic vinyl compound unit whose α-carbon is a quaternary carbon as a main repeating unit. It contains a block copolymer, and the polymer block (A) has a monovalent anion conductive group, or the polyvalent anion conductive group is bonded in a form of cross-linking the polymer blocks (A). And / or an ion conductive binder in which a polyvalent anion conductive group is bonded in a form of cross-linking aromatic vinyl compound units in the polymer block (A).

  In the block copolymer, the polymer block (A) and the polymer block (B) undergo microphase separation, and the polymer block (A) and the polymer block (B) are aggregated. In addition, since the polymer block (A) has an ion conductive group, a continuous phase (ion channel) is formed by the assembly of the polymer blocks (A) and becomes a passage for anions (usually hydroxide ions). Further, the presence of the polymer block (B) makes the block copolymer elastic and flexible as a whole, and formability (assembly property, bonding property) in the production of membrane-electrode assemblies and polymer electrolyte fuel cells. Performance, tightenability, etc.). The flexible polymer block (B) is composed of an alkene unit or a conjugated diene unit.

  The aromatic vinyl compound unit in which the α-carbon is a quaternary carbon includes an aromatic vinyl compound unit in which the hydrogen atom bonded to the α-position carbon atom is substituted with an alkyl group, a halogenated alkyl group or a phenyl group. To do.

The anion conductive group is bonded to the polymer block (A), which is necessary for improving the oxidation stability.
Each anion-conducting group forms a salt with an ammonium group which may be substituted with a C1-C8 alkyl group, a methyl group or an ethyl group bonded to a nitrogen atom, or an acid with a counter ion. Pyridyl group, imidazolium group having methyl or ethyl group bonded to nitrogen atom, imidazolyl group forming salt with acid, phosphonium group optionally substituted with methyl group or ethyl group, hydrogen bonded to nitrogen atom A monovalent or divalent group in which a bond is derived from at least one of two nitrogen atoms of ethylenediamine optionally substituted with a methyl group or an ethyl group, and a hydrogen atom bonded to the nitrogen atom is a methyl group or At least two nitrogen atoms of tri-hexamethylenediamine optionally substituted with an ethyl group A bond is drawn from at least one of two nitrogen atoms of a monovalent or divalent group in which a bond is drawn from one or a methylenediamine in which a hydrogen atom bonded to a nitrogen atom is substituted with a methyl group or an ethyl group. Bonded from at least one of the three nitrogen atoms of diethylene (or bis (trimethylene)) triamine in which the hydrogen atom bonded to the nitrogen atom may be substituted with a methyl group or an ethyl group Includes monovalent, divalent or trivalent groups that are available.

  The present invention also relates to a membrane-electrode assembly using the ion conductive binder and a fuel cell using the membrane-electrode assembly. The present invention also relates to a solution or suspension containing the ion conductive binder.

  The ion conductive binder, membrane-electrode assembly and polymer electrolyte fuel cell of the present invention are economical, environmentally friendly, and excellent in oxidation stability and durability. The ion conductive binder of the present invention is also excellent in moldability.

  Hereinafter, the present invention will be described in detail. The block copolymer constituting the ion conductive binder of the present invention has an aromatic vinyl compound unit in which α-carbon is a quaternary carbon as a main repeating unit, and at least one anion conductive group is (co). The polymer block (A) having is a constituent component.

  The aromatic vinyl compound in which the α-carbon is a quaternary carbon has an alkyl group (a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-containing hydrogen atom bonded to the α-carbon atom). Aromatic vinyl substituted with a butyl group, isobutyl group or tert-butyl group), a halogenated alkyl group having 1 to 4 carbon atoms (chloromethyl group, 2-chloroethyl group, 3-chloroethyl group, etc.) or a phenyl group. It is preferable that it is a type | system | group compound. Examples of the aromatic vinyl compound serving as a skeleton include styrene, vinyl naphthalene, vinyl anthracene, vinyl pyrene, and vinyl pyridine. The hydrogen atom bonded to the aromatic ring of these aromatic vinyl compounds may be substituted with 1 to 3 substituents, and each independently represents an alkyl group having 1 to 4 carbon atoms (methyl group, Ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group or tert-butyl group), C1-C4 halogenated alkyl group (chloromethyl group, 2-chloroethyl group, 3-chloroethyl group, etc.) ) And the like. Specific examples of the aromatic vinyl compound in which the α-carbon is a quaternary carbon include α-methylstyrene. Aromatic vinyl compounds in which the α-carbon is a quaternary carbon may be used alone or in combination of two or more. The form in the case of copolymerizing two or more types may be random copolymerization, block copolymerization, graft copolymerization, or tapered copolymerization.

  The polymer block (A) may contain one or more other monomer units as long as the effects of the present invention are not impaired. Examples of such other monomers include aromatic vinyl compounds [styrene, alkyl groups having 1 to 3 hydrogen atoms bonded to the benzene ring (methyl group, ethyl group, n-propyl group, isopropyl group, n- Styrene, vinylnaphthalene, vinylanthracene, vinylpyrene, etc.) substituted with a butyl group, an isobutyl group or a tert-butyl group], a conjugated diene having 4 to 8 carbon atoms (specific examples are described in the description of the polymer block (B) described later) The same as in the description of the polymer block (B) described later), (meth) acrylate (methyl (meth) acrylate, ethyl (meth) acrylate) Butyl (meth) acrylate), vinyl esters (vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, etc.), vinyl ester Ether (methyl vinyl ether, isobutyl vinyl ether, etc.), and the like. The copolymerization form of the aromatic vinyl compound in which the α-carbon is a quaternary carbon and the other monomer needs to be random copolymerization.

  The aromatic vinyl compound unit in which the α-carbon in the polymer block (A) is a quaternary carbon is used in order to give sufficient oxidation stability to the finally obtained ion conductive binder. It is preferable to occupy 50% by mass or more of A), more preferably 70% by mass or more, and even more preferably 90% by mass or more.

  The molecular weight of the polymer block (A) is appropriately selected depending on the properties of the ion conductive binder, required performance, other polymer components, and the like. When the molecular weight is large, the mechanical properties such as tensile strength of the ion conductive binder tend to be high, and when the molecular weight is small, the electric resistance of the ion conductive binder tends to be small, and the molecular weight is appropriately adjusted according to the required performance. It is important to choose. The number average molecular weight in terms of polystyrene is usually preferably selected from 100 to 1,000,000, more preferably from 1,000 to 100,000.

The block copolymer used in the ion conductive binder of the present invention is a polymer block (A
) And a flexible polymer block (B). The polymer block (A) and the polymer block (B) undergo a microphase separation, and the polymer block (A) and the polymer block (B) have a property of gathering together, and the polymer block (A ) Has an anion-conducting group (co), so that an ion channel as a continuous phase is formed by the assembly of the polymer blocks (A) and becomes a passage for anions (usually hydroxide ions). By having such a polymer block (B), the block copolymer becomes elastic and flexible as a whole, and formability (assembly property, bondability) in the production of membrane-electrode assemblies and polymer electrolyte fuel cells. , Tightenability, etc.). The flexible polymer block (B) here is a so-called rubber-like polymer block having a glass transition point or softening point of 50 ° C. or lower, preferably 20 ° C. or lower, more preferably 10 ° C. or lower.

  Monomers that can constitute the repeating unit constituting the flexible polymer block (B) include alkenes having 2 to 8 carbon atoms, cycloalkenes having 5 to 8 carbon atoms, and vinylcycloalkenes having 7 to 10 carbon atoms. A conjugated diene having 4 to 8 carbon atoms and a conjugated cycloalkadiene having 5 to 8 carbon atoms, a vinylcycloalkene having 7 to 10 carbon atoms in which one of the carbon-carbon double bonds is hydrogenated, and a carbon-carbon double bond A hydrogenated conjugated diene having 4 to 8 carbon atoms, a hydrogenated conjugated cycloalkadiene having one hydrogenated carbon-carbon double bond, (meth) acrylic acid ester ((meth)) Methyl acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, etc.), vinyl esters (vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, etc.), vinyl Ether (methyl vinyl ether, isobutyl vinyl ether, etc.), and the like. These may be used alone or in combination. The form in the case of copolymerizing two or more types may be random copolymerization, block copolymerization, graft copolymerization, or tapered copolymerization. Further, when the monomer to be used for (co) polymerization has two carbon-carbon double bonds, any of them may be used for the polymerization, and in the case of a conjugated diene, it is a 1,2-bond. 1,4-bonds may be used, and the ratio of 1,2-bonds to 1,4-bonds is not particularly limited as long as the glass transition point or softening point is 50 ° C. or lower.

When the repeating unit constituting the polymer block (B) has a carbon-carbon double bond as in the case of a vinylcycloalkene unit, a conjugated diene unit, or a conjugated cycloalkadiene unit, the present invention From the standpoint of improving the power generation performance of the membrane-electrode assembly using the ion conductive binder of the above, improvement in heat deterioration resistance, etc., it is preferable that 30 mol% or more of such carbon-carbon double bonds are hydrogenated, More preferably, 50 mol% or more is hydrogenated, and more preferably 80 mol% or more is hydrogenated. The hydrogenation rate of the carbon-carbon double bond can be calculated by a commonly used method, for example, iodine value measurement method, ¹ H-NMR measurement or the like.

  The polymer block (B) is an alkene having 2 to 8 carbon atoms from the viewpoint of giving the resulting block copolymer elasticity and, in turn, good moldability in the production of a membrane-electrode assembly and a polymer electrolyte fuel cell. Unit, cycloalkene unit having 5 to 8 carbon atoms, vinylcycloalkene unit having 7 to 10 carbon atoms, conjugated diene unit having 4 to 8 carbon atoms, conjugated cycloalkadiene unit having 5 to 8 carbon atoms, carbon-carbon double 7 to 10 carbon cycloalkene units having some or all of the hydrogenated hydrogen atoms, 4 to 8 carbon conjugated diene units having some or all of the carbon-carbon double bonds hydrogenated, and carbon -A polymer block comprising at least one repeating unit selected from conjugated cycloalkadiene units having 5 to 8 carbon atoms in which some or all of the carbon double bonds are hydrogenated. Preferably, the alkene unit having 2 to 8 carbon atoms, the conjugated diene unit having 4 to 8 carbon atoms, and the conjugated diene unit having 4 to 8 carbon atoms in which some or all of the carbon-carbon double bonds are hydrogenated are selected. More preferably, the polymer block is composed of at least one repeating unit, and the alkene unit having 2 to 6 carbon atoms, the conjugated diene unit having 4 to 8 carbon atoms, and a part or all of the carbon-carbon double bonds are included. It is even more preferable that the polymer block is composed of at least one repeating unit selected from hydrogenated conjugated diene units having 4 to 8 carbon atoms. In the above, the most preferable alkene unit having 2 to 6 carbon atoms is an isobutene unit, and the most preferable conjugated diene unit is a 1,3-butadiene unit and / or an isoprene unit.

  As the alkene having 2 to 8 carbon atoms, ethylene, propylene, 1-butene, 2-butene, isobutene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, 1-heptene, 2-heptene, 1 -Octene, 2-octene, and the like. Examples of the cycloalkene having 5 to 8 carbon atoms include cyclopentene, cyclohexene, cycloheptene, and cyclooctene. Examples of the vinylcycloalkene having 7 to 10 carbon atoms include vinylcyclopentene, vinylcyclohexene, Examples thereof include vinylcycloheptene and vinylcyclooctene. Examples of the conjugated diene having 4 to 8 carbon atoms include 1,3-butadiene, 1,3-pentadiene, isoprene, 1,3-hexadiene, 2,4-hexadiene, 2 , 3-Dimethyl-1,3-butadiene, 2-ethyl-1,3-butyl Diene, 1,3-heptadiene, 1,4-heptadiene, 3,5-heptadiene and the like, cyclopentadiene, 1,3-cyclohexadiene, and the like as a conjugated cycloalkadiene having 5 to 8 carbon atoms.

  In addition to the above monomers, the polymer block (B) is a unit of another monomer, such as styrene, within a range that does not impair the purpose of the polymer block (B) that gives elasticity to the block copolymer. Aromatic vinyl compounds such as vinyl naphthalene; units such as halogen-containing vinyl compounds such as vinyl chloride may be included. In this case, the copolymerization form of the monomer and other monomer needs to be random copolymerization. The amount of such other monomer used is preferably less than 50% by weight, more preferably less than 30% by weight, based on the total of the above monomers and other monomers. It is still more preferable that it is less than mass%.

  Although the structure of the block copolymer which has a polymer block (A) and a polymer block (B) as a structural component is not specifically limited, ABA type | mold triblock copolymer, BAB, as an example Type triblock copolymer, ABA type triblock copolymer, or a mixture of BAB type triblock copolymer and AB type diblock copolymer, ABA type B-type tetrablock copolymer, A-B-A-B-A type pentablock copolymer, B-A-B-A-B type pentablock copolymer, (AB) nX-type star copolymer Examples thereof include a polymer (X represents a coupling agent residue), (BA) nX type star copolymer (X represents a coupling agent residue), and the like. These block copolymers may be used alone or in combination of two or more.

  The mass ratio of the polymer block (A) and the polymer block (B) is preferably 95: 5 to 5:95, more preferably 90:10 to 10:90, and 50:50 to 10 : 90 is even more preferable. When this mass ratio is 95: 5 to 5:95, it is advantageous for the ion channel formed by the polymer block (A) to become a cylindrical or continuous phase by microphase separation, which is practically sufficient. Anionic conductivity is exhibited, and the proportion of the polymer block (B) that is hydrophobic is appropriate and has excellent water resistance, so that the ion conductive binder can be prevented from flowing out during power generation.

The block copolymer constituting the ion conductive binder of the present invention may contain another polymer block (C) different from the polymer block (A) and the polymer block (B).
The polymer block (C) is not particularly limited as long as it is a component that undergoes microphase separation from the polymer block (A) and the polymer block (B). Examples of the monomer constituting the polymer block (C) include aromatic vinyl compounds [styrene, alkyl groups having 1 to 3 hydrogen atoms bonded to the benzene ring (methyl group, ethyl group, n-propyl group). Styrene, vinyl naphthalene, vinyl anthracene, vinyl pyrene, etc. substituted with isopropyl group, n-butyl group, isobutyl group or tert-butyl group], conjugated dienes having 4 to 8 carbon atoms (specific examples are the aforementioned polymers) (Same as in the description of the block (B)), alkene having 2 to 8 carbon atoms (specific examples are the same as in the description of the polymer block (B) described above), (meth) acrylic acid ester ((meth) acrylic acid Methyl, ethyl (meth) acrylate, butyl (meth) acrylate, etc.), vinyl esters (vinyl acetate, vinyl propionate, vinyl butyrate, pivalic acid) Sulfonyl, etc.), vinyl ethers (methyl vinyl ether, isobutyl vinyl ether, etc.), and the like. The monomer constituting the polymer block (C) may be one kind or plural kinds.

When the polymer block (C) is microphase-separated from the polymer block (A) and the polymer block (B) and does not substantially contain an ionic group and has a function of acting as a constrained phase, this is required. The block copolymer used in the present invention having the polymer block (C) tends to be excellent in form stability, durability and mechanical properties under wet conditions. Preferable examples of the monomer constituting the polymer block (C) in this case include the aromatic vinyl compounds described above. Moreover, the above-mentioned function can be imparted by making the polymer block (C) crystalline.

  When the above-mentioned function depends on the aromatic vinyl compound unit, the aromatic vinyl compound unit in the polymer block (C) preferably occupies 50% by mass or more of the polymer block (C), and 70% by mass. %, More preferably 90% by mass or more. From the same viewpoint as described above, it is desirable that units other than the aromatic vinyl compound unit that can be included in the polymer block (C) are randomly polymerized.

  As a particularly preferable example from the viewpoint of causing the polymer block (C) to microphase-separate from the polymer block (A) and the polymer block (B) and to function as a constrained phase, a polystyrene block; a poly p-methylstyrene block, a poly Polystyrene block such as p- (t-butyl) styrene block; copolymer block composed of two or more kinds of styrene, p-methylstyrene and p- (t-butyl) styrene of any mutual ratio; crystalline water Examples include 1,4-polybutadiene block; crystalline polyethylene block; crystalline polypropylene block and the like.

  As a form in case the block copolymer used by this invention contains a polymer block (C), an ABC type triblock copolymer, an ABCA type tetrablock copolymer, A -B-A-C type tetrablock copolymer, B-A-B-C type tetrablock copolymer, A-B-C-B type tetrablock copolymer, C-A-B-A-C Type pentablock copolymer, CBACBBC type pentablock copolymer, ACCBCA type pentablock copolymer, ACCBAA type pentablock copolymer Block copolymer, A-B-C-A-B type pentablock copolymer, A-B-C-A-C type pentablock copolymer, A-B-C-B-C type pentablock copolymer Polymer, ABACBBC type pentablock copolymer, ABBACB type pentablock copolymer B-A-B-A-C type pentablock copolymer, B-A-B-C-A type pentablock copolymer, B-A-B-C-B type pentablock copolymer, etc. are mentioned. It is done.

  When the block copolymer constituting the ion conductive binder of the present invention contains a polymer block (C), the proportion of the polymer block (C) in the block copolymer is preferably 40% by mass or less, It is more preferably 35% by mass or less, and further preferably 30% by mass or less.

  Although the number average molecular weight of the block copolymer used in the present invention in a state where the anion conductive group is not introduced is not particularly limited, the number average molecular weight in terms of polystyrene is usually 10,000 to 2,000,000. Preferably, 15,000 to 1,000,000 is more preferable, and 20,000 to 500,000 is even more preferable.

  The block copolymer constituting the ion conductive binder of the present invention needs to have an anion conductive group in the polymer block (A). Examples of the anion when referring to anion conductivity in the present invention include hydroxide ions. The anion conductive group is not particularly limited as long as the membrane-electrode assembly produced using the ion conductive binder can express sufficient anion conductivity. Can be mentioned. The introduction position of the anion conductive group is the polymer block (A) because it is particularly effective for improving the oxidative stability of the entire block copolymer.

In the above formula, R ^{1 to} R ³ each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, R ^{4 to} R ⁹ and R ¹¹ each independently represents a hydrogen atom, a methyl group or an ethyl group, R ¹⁰ represents a methyl group or an ethyl group, X ⁻ represents a hydroxide ion or an acid anion, m represents an integer of 2 to 6, and n represents 2 or 3. In the above, the alkyl group having 1 to 8 carbon atoms is methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, 2-ethylhexyl. Groups and the like. There is no particular limitation on the anion, for example, a halogen ion (particularly chloride ^{_{ion), 1 / 2SO 4 2-,}} HSO 4 -, may be mentioned p- toluenesulfonate anion.
Moreover, in the above, when R < ¹ > -R < ⁹ > and R < ¹¹ > are a methyl group or an ethyl group and X < ^- > is a hydroxide ion, since high anion conductivity can be expressed, it is preferable. R ^{1 to} R ¹¹ are more preferably a methyl group.

  There are no particular restrictions on the position at which the anion conductive group is introduced into the polymer block (A), and even if it is introduced into an aromatic vinyl compound unit in which the α-carbon is a quaternary carbon, the other units described above It may be introduced into the body unit, but is most preferably introduced into the aromatic ring of the aromatic vinyl compound unit in which the α-carbon is a quaternary carbon from the viewpoint of improving the oxidation stability. At this time, when the introduced anion conductive group is a monovalent group such as (1) to (8) in the above formula, the group is bonded to the polymer block (A). Is a polyvalent group such as (9) to (13) in the above formula, the group is bonded in a form that crosslinks the polymer blocks (A), or the polymer block In (A), the aromatic vinyl compound units are bonded in a form of crosslinking.

  The amount of anion-conducting group introduced is appropriately selected depending on the required performance of the resulting block copolymer, etc., but exhibits sufficient anion conductivity for use as an ion-conducting binder for solid polymer fuel cells In general, the amount is preferably such that the ion exchange capacity of the block copolymer is 0.30 meq / g or more, and more preferably 0.40 meq / g or more. . The upper limit of the ion exchange capacity of the block copolymer is preferably 3.0 meq / g or less because if the ion exchange capacity is too large, the hydrophilicity tends to increase and the water resistance becomes insufficient.

  The production method of the block copolymer used in the present invention is roughly classified into the following two methods. That is, (1) a method in which a block copolymer having no anion conductive group is first prepared and then anion conductive groups are bonded, and (2) block copolymerization using a monomer having an anion conductive group. This is a method for producing a coalescence.

First, the first manufacturing method will be described.
Depending on the type, molecular weight, etc. of the monomer constituting the polymer block (A) or (B), the production method of the polymer block (A) or (B) can be a radical polymerization method, an anionic polymerization method, a cationic polymerization method, The method is appropriately selected from coordination polymerization methods and the like, but from the viewpoint of industrial ease, a radical polymerization method, an anionic polymerization method or a cationic polymerization method is preferably selected. In particular, the so-called living polymerization method is preferred from the viewpoint of molecular weight, molecular weight distribution, polymer structure, ease of bonding with the polymer block (B) or (A) comprising a flexible component, and specifically, a living radical polymerization method. Or a living anionic polymerization method and a living cation polymerization method are preferable.

  Specific examples of the production method include a method for producing a block copolymer comprising a polymer block (A) made of poly (α-methylstyrene) and a polymer block (B) made of polyconjugated diene, and poly (α A method for producing a block copolymer comprising a polymer block (A) composed of -methylstyrene) and a polymer block (B) composed of polyisobutene will be described. In this case, it is preferable to produce by a living anionic polymerization method or a living cationic polymerization method from the viewpoint of industrial ease, molecular weight, molecular weight distribution, ease of bonding between the polymer block (A) and the polymer block (B), etc. The following specific synthesis examples are shown.

(1) A method of obtaining an ABA type block copolymer by sequentially polymerizing α-methylstyrene under a temperature condition of −78 ° C. after conjugated diene polymerization using a dianionic initiator in a tetrahydrofuran solvent (Macromolecules , (1969), 2 (5), 453-458),
(2) After bulk polymerization of α-methylstyrene using an anionic initiator, conjugated dienes are sequentially polymerized, and then a coupling reaction is performed with a coupling agent such as tetrachlorosilane. (AB) nX Method for obtaining a mold block copolymer (Kautsch. Gummi,
Kunstst. , (1984), 37 (5), 377-379; Po
lym. Bull. , (1984), 12, 71-77),
(3) An organic lithium compound in a nonpolar solvent is used as an initiator, and a concentration of 5 to 50% by mass at a temperature of −30 ° C. to 30 ° C. in the presence of a polar compound having a concentration of 0.1 to 10% by mass. A polymer obtained by polymerizing α-methylstyrene, a conjugated diene is polymerized to the resulting living polymer, and then a coupling agent is added to obtain an ABA block copolymer.

(4) A concentration of 5 to 50% by mass at a temperature of −30 ° C. to 30 ° C. in the presence of a polar compound having a concentration of 0.1 to 10% by mass using an organolithium compound in a nonpolar solvent as an initiator. Α-methylstyrene is polymerized, the resulting living polymer is polymerized with a conjugated diene, and the resulting α-methylstyrene polymer block and conjugated diene polymer block are formed into a polymer block (C ) To obtain an ABC type block copolymer,
(5) Cationic polymerization of isobutene in the presence of Lewis acid using a bifunctional organic halogen compound at -78 ° C in a mixed solvent of halogenated hydrocarbon and hydrocarbon, followed by addition of diphenylethylene, Further, after adding Lewis acid, α-methylstyrene is polymerized to obtain an ABA type block copolymer (Macromolecules, (1995), 28, 4893-4898), and (6) halogenated carbonization. In a mixed solvent of hydrogen and hydrocarbon at −78 ° C., using a monofunctional organic halogen compound, α-methylstyrene is polymerized in the presence of Lewis acid, and then Lewis acid is further added to polymerize isobutene. After that, a coupling reaction is performed with a coupling agent such as 2,2-bis- [4- (1-phenylethenyl) phenyl] propane, and the ABA block Method for obtaining a polymer (Polym.
Bull. , (2000), 45, 121-128)

When producing a block copolymer comprising as a component a polymer block (A) comprising poly (α-methylstyrene) and a polymer block (B) comprising a conjugated diene compound, a specific method for producing the block copolymer Among these, the methods (3) and (4) are preferable, and the method (3) is particularly preferable.
When producing a block copolymer comprising a polymer block (A) made of poly (α-methylstyrene) and a polymer block (B) made of isobutene as a component, a known method shown in (5) or (6) Is adopted.

  Next, a method for introducing an anion conductive group into the obtained block copolymer will be described. The introduction of the anion conductive group can be performed by a known method. For example, the resulting block copolymer is chloromethylated, then reacted with an amine or phosphine, and further, chlorine ions are replaced with hydroxide ions or other acid anions as necessary.

  The chloromethylation method is not particularly limited, and a known method can be used. For example, a method of adding a chloromethylating agent and a catalyst to a solution or suspension of the block copolymer in an organic solvent and chloromethylating can be used. Examples of the organic solvent include halogenated hydrocarbons such as chloroform and dichloroethane, but are not limited thereto. As the chloromethylating agent, chloromethyl ethyl ether or hydrochloric acid-paraformaldehyde can be used, and as the catalyst, tin chloride, zinc chloride or the like can be used.

The method for reacting the chloromethylated block copolymer with amine or phosphine is not particularly limited, and a known method can be used. For example, a solution or suspension of the obtained chloromethylated block copolymer in an organic solvent, or a film formed by a known method from such a solution or suspension, amine or phosphine is used as it is or as necessary. A method of allowing the reaction to proceed by adding it as a solution in an organic solvent can be used. Examples of the organic solvent for preparing a solution or suspension in the organic solvent include methanol and acetone, but are not limited thereto.
The amine and phosphine are not particularly limited, but those shown below can be preferably used.

In the above ^{formula, R 1 ~R 3, R 6} ~R 11, m and n are defined as above. That is, R ^{1 to} R ³ are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, R ^{6 to} R ^{9 and} R ¹¹ are each independently a hydrogen atom, a methyl group, or an ethyl group, and R ¹⁰ Is a methyl group or an ethyl group, m is an integer of 2 to 6, and n is 2 or 3. R ^{1 to} R ³ , R ^{6 to} R ^{9 and} R ¹¹ are preferably each independently a methyl group or an ethyl group, and R ^{1 to} R ^{3 and} R ^{6 to} R ¹¹ are more preferably a methyl group.

Reaction of the chloromethylated block copolymer with an amine or phosphine introduces an anion-conducting group as already mentioned. Here, when monoamine (1) or phosphine (2) is used, an anion conductive group is introduced into the polymer block (A), but diamine (3) or (4), triamine (5), etc. When the polyvalent amine is used, it may be introduced as a monovalent anion conductive group in the polymer block (A), or may be introduced as a polyvalent anion conductive group. It is considered that the aromatic vinyl compound units may be crosslinked with each other in the polymer block (A).
^Further, and when R 1 to R ³ is an alkyl group having 1 to 8 carbon ^atoms, when R 6 to R ⁹ and ^{R 11} is a methyl group or an ethyl group, anion-conducting group is a quaternary ammonium Group or quaternary phosphonium group.

  Since the anion conductive group introduced above has a chlorine ion as an acid anion, it is converted into a hydroxide ion or another acid anion, preferably a hydroxide ion, if necessary. A method for converting to other ions is not particularly limited, and a known method can be used. For example, when converting to hydroxide ions, a method of immersing a block copolymer into which an anion conductive group is introduced in an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution can be exemplified.

As described above, the amount of the anion conductive group introduced is preferably such that the ion exchange capacity of the block copolymer is 0.30 meq / g or more, such that it is 0.40 meq / g or more. More preferably, it is an amount. Thereby, practical anion conducting performance can be obtained. The ion exchange capacity of the block copolymer into which the anion conductive group is introduced can be measured by using analytical means such as titration method, infrared spectrum measurement, nuclear magnetic resonance spectrum ( ¹ H-NMR spectrum) measurement. .

The second production method of the block copolymer used in the present invention is a method for producing a block copolymer using at least one monomer having an anion conductive group.
As the monomer having an anion conductive group, the following groups can be used.

In formula, R < ¹² >, R <^14> and R < ¹⁶ > represent a hydrogen atom, a C1-C4 alkyl group, a C1-C4 halogenated alkyl group, or a phenyl group, and R < ¹³ > has a hydrogen atom or C1-C1. 8 represents an alkyl group, R ¹⁵ and R ¹⁷ represent a hydrogen atom, a methyl group or an ethyl group, and X ⁻ represents a hydroxide ion or an acid anion. In the above, the alkyl group having 1 to 4 carbon atoms is methyl group, ethyl group, n-propyl group, isopropyl group, isobutyl group, etc., and the halogenated alkyl group having 1 to 4 carbon atoms is chloromethyl group, chloroethyl group, A chloropropyl group etc. are mentioned. Moreover, as a C1-C8 alkyl group, a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, 2-ethylhexyl group Etc. The acid anion is not particularly limited, for example, a halogen ion (particularly chloride ^{_{ion), 1 / 2SO 4 2-,}} HSO 4 -, may be mentioned p- toluenesulfonate anion. R ^{12 to} R ¹⁷ are preferably a methyl group or an ethyl group, and more preferably a methyl group. In the above formula (2), the —C (R ¹⁴ ) ═CH ₂ group is preferably bonded to the 4-position or the 2-position.
Among the monomers having an anion conductive group described above, a monomer represented by the formula (1) in which R ¹³ is a methyl group or an ethyl group, particularly a methyl group, is particularly preferable.

  In addition to the block copolymer used by this invention, the ion conductive binder of this invention may contain the softening agent in the range which does not impair the effect of this invention as needed. Softeners include petroleum-based softeners such as paraffinic, naphthenic or aroma-based process oils, paraffin, vegetable oil-based softeners, plasticizers, etc., and these may be used alone or in combination of two or more. it can.

  The ion-conductive binder of the present invention may further include various additives such as phenol-based stabilizers, sulfur-based stabilizers, phosphorus-based stabilizers, and light stabilizers, as long as they do not impair the effects of the present invention. , Antistatic agents, mold release agents, flame retardants, foaming agents, pigments, dyes, whitening agents, carbon fibers and the like may be used alone or in combination of two or more. Specific examples of the stabilizer include 2,6-di-t-butyl-p-cresol, pentaerystyryl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 1 , 3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, octadecyl-3- (3,5-di-tert-butyl-4-hydroxy) Phenyl) propionate, triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy- 3,5-di-t-butylanilino) -1,3,5-triazine, 2,2, -thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propi Onate], N, N′-hexamethylenebis (3,5-di-tert-butyl-4-hydroxy-hydrodinamamide), 3,5-di-tert-butyl-4-hydroxy-benzylphosphonate-diethyl ester, tris -(3,5-di-tert-butyl-4-hydroxybenzyl) -isocyanurate, 3,9-bis {2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy ] 1,1-dimethylethyl} -2,4,8,10-tetraoxaspiro [5,5] undecane and other fail stabilizers; pentaerythrityltetrakis (3-laurylthiopropionate), distearyl Sulfur systems such as 3,3′-thiodipropionate, dilauryl 3,3′-thiodipropionate, dimyristyl 3,3′-thiodipropionate Stabilizer; trisnonylphenyl phosphite, tris (2,4-di-t-butylphenyl) phosphite, diasteryl pentaerythritol diphosphite, bis (2,6-di-t-butyl-4-methylphenyl) And phosphorus stabilizers such as pentaerythritol diphosphite. These stabilizers may be used alone or in combination of two or more.

  The ion conductive binder of the present invention may further contain an inorganic filler as long as it does not impair the effects of the present invention. Specific examples of such inorganic fillers include talc, calcium carbonate, silica, glass fiber, mica, kaolin, titanium oxide, montmorillonite, and alumina.

  From the viewpoint of ion conductivity, the content of the block copolymer in the ion conductive binder of the present invention is preferably 50% by mass or more, more preferably 70% by mass or more, and 90% by mass or more. Is more preferable.

The ion conductive binder of the present invention is used in a catalyst layer constituting a gas diffusion electrode of a polymer electrolyte fuel cell, or is used for a joining surface between an electrolyte membrane and a catalyst layer. The ion conductive binder is preferably used for electrodes on both sides of the membrane-electrode assembly, but may be used for only one of them.

  As a method of attaching the ion conductive binder of the present invention to the surface of a catalyst carrier carrying a catalyst, binding the catalyst carriers together, and joining this to a gas diffusion layer or an electrolyte membrane, an ion conductive binder is used. A catalyst paste prepared by mixing a solution or suspension of the above with raw material particles such as a conductive catalyst carrier carrying a catalyst may be applied to a gas diffusion layer or an electrolyte membrane, or a catalyst for a gas diffusion electrode formed in advance. The layer may be impregnated with a solution containing an ion conductive binder.

  The solvent used for the solution or suspension of the ion conductive binder of the present invention is not particularly limited as long as it does not destroy the structure of the block copolymer. Specifically, halogenated hydrocarbons such as methylene chloride, aromatic hydrocarbon solvents such as toluene, xylene, and benzene, linear aliphatic hydrocarbons such as hexane and heptane, and cyclic aliphatic carbonization such as cyclohexane. Hydrogen, ethers such as tetrahydrofuran, alcohols such as methanol, ethanol, propanol, isopropanol, acetonitrile, nitromethane, dimethyl sulfoxide, N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, etc. It can be illustrated. These solvents can be used alone or in combination of two or more. Moreover, it is good also as a mixed solution with water to such an extent that the solubility or suspension property of an ion conductive binder is not impaired.

  The density | concentration of the solution or suspension containing an ion conductive binder should just be a density | concentration in which a suitable membrane | film | coat is easy to be formed on the catalyst surface of a catalyst layer, and it is preferable that it is normally 3 mass%-10 mass%. If this concentration is too high, the thickness of the film formed on the catalyst surface will be too large, and diffusion of the reaction gas to the catalyst will be hindered, or a uniform catalyst layer will not be formed, and the utilization efficiency of the catalyst will be reduced. As a result, the output of the fuel cell may decrease. Also, if this concentration is too low, the viscosity of the solution or suspension is too small, and when applied to the gas diffusion layer, it penetrates deeply into the gas diffusion layer and inhibits gas diffusibility. There is.

  As another method for attaching the catalyst by attaching the ion conductive binder of the present invention to the surface of the catalyst carrier of the catalyst layer, the ion conductive binder powder is used as a raw material for a conductive catalyst carrier or the like carrying the catalyst. The method of mixing with particle | grains and electrostatically applying to a gas diffusion layer or an electrolyte membrane is mentioned.

  As a method of using the ion conductive binder of the present invention on the joint surface between the electrolyte membrane and the catalyst layer, a solution or suspension of the ion conductive binder is applied to the catalyst layer surface formed on the electrolyte membrane or the gas diffusion electrode. Then, the electrolyte membrane and the gas diffusion electrode are bonded together and thermocompression bonded as necessary, or the fine powder of the ion conductive binder is electrostatically applied to the surface of the catalyst layer formed on the electrolyte membrane or the gas diffusion electrode, and the electrolyte A method in which the membrane and the electrode are bonded together and thermocompression bonding is performed at a temperature higher than the softening temperature of the ion conductive binder is exemplified.

  The solution concentration in the case of using a solution containing an ion conductive binder at the joining interface between the electrolyte membrane and the catalyst layer is 3% by mass to 10% by mass for ensuring the adhesion between the polymer electrolyte membrane and the gas diffusion electrode. preferable. If this concentration is too low, the bonding between the electrolyte membrane and the gas diffusion electrode may be incomplete. Moreover, when this density | concentration is too high, the applicability | paintability to the joint surface of a gas diffusion layer may fall, or the permeability to a detail may fall.

  Next, a membrane-electrode assembly using the ion conductive binder of the present invention will be described. The production of the membrane-electrode assembly is not particularly limited, and a known method can be applied. For example, a catalyst paste containing an ion conductive binder is applied on the gas diffusion layer by a printing method or a spray method and dried. To form a joined body of the catalyst layer and the gas diffusion layer, and then to join the two pairs of joined bodies with the catalyst layer on the inside and hot press on both sides of the electrolyte membrane, or the above catalyst paste Is applied to both sides of the electrolyte membrane by a printing method or a spray method, dried to form catalyst layers, and a gas diffusion layer is pressure-bonded to each catalyst layer by hot pressing or the like. As yet another production method, a solution or suspension containing an ion conductive binder is applied to both surfaces of the electrolyte membrane and / or the catalyst layer surfaces of the two pairs of gas diffusion electrodes, and the electrolyte membrane and the catalyst layer surface are bonded together, There is a method of joining by pressure bonding or the like. In this case, the solution or suspension may be applied to either the electrolyte membrane or the catalyst layer surface, or may be applied to both. As another manufacturing method, first, the catalyst paste is applied to a base film made of polytetrafluoroethylene (PTFE) and dried to form a catalyst layer, and then two pairs of base films on the base film are formed. There is a method in which a catalyst layer is transferred to both sides of an electrolyte membrane by thermocompression bonding, a base film is peeled to obtain a joined body of the electrolyte membrane and the catalyst layer, and a gas diffusion layer is crimped to each catalyst layer by hot pressing. is there. In these methods, these methods may be performed in a state in which the anion conductive group is converted to a salt such as chloride, and a treatment for returning to a hydroxide type by an alkali treatment after bonding may be performed.

  In the membrane-electrode assembly of the present invention, the ion conductive binder of the present invention is used for at least one of the electrode catalyst layer and the bonding surface between the gas diffusion electrode and the electrolyte membrane. It is preferably used for both, and in this case, the effect of improving the oxidation stability of the fuel cell is remarkable.

  As the electrolyte membrane constituting the membrane-electrode assembly, for example, polychloromethylstyrene is reacted with a tertiary amine to form a quaternary ammonium salt, and in the form of a hydroxide if necessary. be able to. Moreover, you may produce an electrolyte membrane from the block copolymer which comprises the ion conductive binder of this invention. In order to further enhance the adhesion between the electrolyte membrane and the gas diffusion electrode, it is preferable to use an electrolyte membrane formed from the same material as the polymer in the ion conductive binder used for the gas diffusion electrode.

  The constituent material of the catalyst layer of the membrane-electrode assembly is not particularly limited as the conductive material / catalyst support, and examples thereof include carbon materials. Examples of the carbon material include carbon black such as furnace black, channel black, and acetylene black, activated carbon, graphite, and the like. These may be used alone or in combination of two or more. The catalyst metal may be any metal that promotes the oxidation reaction of fuel such as hydrogen and methanol and the reduction reaction of oxygen, such as platinum, gold, silver, palladium, iridium, rhodium, ruthenium, iron, Cobalt, nickel, chromium, tungsten, manganese, palladium, etc., or alloys thereof, for example, platinum-ruthenium alloys are mentioned. Of these, platinum and platinum alloys are often used. The particle size of the metal serving as a catalyst is usually 10 to 300 angstroms. When these catalysts are supported on a conductive material such as carbon / catalyst support, the amount of catalyst used is small and it is advantageous in terms of cost. The catalyst layer may contain a water repellent as necessary. Examples of the water repellent include various thermoplastic resins such as polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene copolymer, and polyetheretherketone.

  The gas diffusion layer of the membrane-electrode assembly is made of a material having conductivity and gas permeability, and examples of such a material include porous materials made of carbon fibers such as carbon paper and carbon cloth. Moreover, in order to improve water repellency, this material may be subjected to water repellency treatment.

A polymer electrolyte fuel obtained by inserting the membrane-electrode assembly obtained by the above-described method between a conductive separator material that also serves as a gas supply flow path to the electrode and the electrode chamber separation. A battery is obtained. The membrane-electrode assembly of the present invention uses a pure hydrogen type using hydrogen as a fuel gas, a methanol reforming type using hydrogen obtained by reforming methanol, and hydrogen obtained by reforming natural gas. Natural gas reforming type, gasoline reforming type using hydrogen obtained by reforming gasoline, direct methanol type using methanol directly, etc. can be used as a membrane-electrode assembly for polymer electrolyte fuel cells. is there.
A fuel cell using the membrane-electrode assembly obtained by the above method is excellent in chemical stability, has little deterioration in power generation characteristics over time, and can be used stably for a long time.

EXAMPLES Hereinafter, although an Example, a comparative example, and a reference example are given and this invention is demonstrated further more concretely, this invention is not limited by these.
Reference example 1
Production of block copolymer comprising poly (α-methylstyrene) (polymer block (A)) and hydrogenated polybutadiene (polymer block (B)) Same as previously reported method (Japanese Patent Laid-Open No. 2001-172324) In this way, a poly (α-methylstyrene) -b-polybutadiene-poly (α-methylstyrene) type triblock copolymer (hereinafter abbreviated as mSEBmS) was synthesized. The number average molecular weight (GPC measurement, polystyrene conversion) of the obtained mSEBmS is 74000, the 1,4-bond content determined from ¹ H-NMR measurement is 56%, and the content of α-methylstyrene unit is 28.6. It was mass%. Further, it was found by composition analysis by ¹ H-NMR spectrum measurement that α-methylstyrene was not substantially copolymerized in the polybutadiene block.
A cyclohexane solution of synthesized mSEBmS was prepared and charged into a pressure-resistant vessel that had been sufficiently purged with nitrogen. Then, a hydrogenation reaction was performed at 80 ° C. for 5 hours in a hydrogen atmosphere using a Ni / Al Ziegler hydrogenation catalyst. The poly (α-methylstyrene) -b-hydrogenated polybutadiene-b-poly (α-methylstyrene) type triblock copolymer (hereinafter abbreviated as HmSEBmS) was obtained. The hydrogenation proportion of the resulting HmSEBmS was calculated by ¹ H-NMR spectrum measurement, it was 99.8%.

Example 1
(1) Production of HmSEBmS having quaternary ammonium hydroxide group 100 g of the block copolymer (HmSEBmS) obtained in Reference Example 1 was vacuum-dried in a glass reaction vessel equipped with a stirrer for 1 hour, and then purged with nitrogen. After that, 650 ml of chloroform was added and dissolved by stirring at 35 ° C. for 2 hours. After dissolution, 135 ml of chloromethyl ethyl ether and 5.7 ml of tin tetrachloride were added and stirred at 35 ° C. for 9 hours. Next, the reaction solution was added to 4 L of methanol, and the precipitate was washed and dried to obtain chloromethylated HmSEBmS. The chloromethylation rate of chloromethylated HmSEBmS was 59.0 mol% of α-methylstyrene units from ¹ H-NMR analysis.
Next, chloromethylated HmSEBmS was dissolved in toluene, cast on a polytetrafluoroethylene sheet and sufficiently dried at room temperature to obtain a cast film having a thickness of 70 μm.
Next, the chloromethyl group was aminated by immersing the obtained cast film in a mixed solution of 30% trimethylamine aqueous solution and acetone in a volume ratio of 1: 1 at room temperature for 24 hours.
Finally, the aminated HmSEBmS membrane was immersed in a 0.5N-NaOH aqueous solution at room temperature for 5 hours for ion exchange to obtain an HmSEBmS membrane having a quaternary ammonium hydroxide group. The film thickness was 100 μm, and the ion exchange capacity was 1.26 meq / g in terms of the value obtained from ¹ H-NMR measurement.

(2) Production of single cell for polymer electrolyte fuel cell An electrode for a polymer electrolyte fuel cell was produced by the following procedure. The Pt catalyst-supported carbon is mixed with the chloroform / isobutyl alcohol solution (chloroform: isobutyl alcohol = 7: 3, 4% by mass) of the HmSEBmS film having the quaternary ammonium hydroxide group obtained in (1) and dispersed uniformly. A prepared paste was prepared. This paste was uniformly applied to one side of a water-repellent treated carbon paper and left for several hours to produce a carbon paper electrode. The amount of Pt supported on the prepared electrode and the amount of HmSEBmS having a quaternary ammonium hydroxide group were both 1.0 mg / cm ² . Next, the electrolyte membrane (10 cm × 10 cm) produced in (1) is sandwiched between carbon paper electrodes (5.0 cm × 5.0 cm) so that the membrane and the catalyst surface face each other, and the outer side of the two heat resistant films And a membrane-electrode assembly was prepared by sandwiching in turn between two stainless plates and hot pressing (60 ° C., 80 kg / cm ² , 2 min).
The membrane-electrode assembly produced above (with the heat-resistant film and stainless steel plate removed) is sandwiched between two conductive separators that also serve as gas supply channels, and the outside of the membrane-electrode assembly is two sheets. An evaluation cell for a polymer electrolyte fuel cell was produced by sandwiching in turn between an electric plate and two clamping plates. In addition, a gasket was disposed between each membrane-electrode assembly and the separator in order to prevent gas leakage from a step corresponding to the thickness of the electrode.

Example 2
(1) Production of HmSEBmS having quaternary ammonium hydroxide group In Example 1, chloromethylated HmSEBmS was obtained in the same manner as in Example 1 except that the reaction time of chloromethylation was 20 minutes. The chloromethylation rate of chloromethylated HmSEBmS was 23.0 mol% of α-methylstyrene units from ¹ H-NMR analysis. Next, by the same method as in Example 1 (1), amination and ion exchange were performed to obtain a HmSEBmS film having a quaternary ammonium hydroxide group. The film thickness was 100 μm, and the ion exchange capacity was 0.49 meq / g in terms of the value obtained from ¹ H-NMR measurement.
(2) Production of single cell for polymer electrolyte fuel cell An electrode was produced in the same manner as in Example 1 (2) except that HmSEBmS having a quaternary ammonium hydroxide group prepared in (1) above was used. Next, a membrane-electrode assembly and an evaluation cell for a polymer electrolyte fuel cell were produced from the membrane produced in Example 1 (1) and the above electrode by the same method as in Example 1 (2). The amount of Pt supported on the produced electrode and the amount of HmSEBmS having an ammonium hydroxide group were both 0.95 mg / cm ² .

Comparative Example 1
Preparation of SEBS having quaternary ammonium hydroxide group 100 g of SEBS (styrene- (ethylene-butylene) -styrene) block copolymer [“Septon 8007” manufactured by Kuraray Co., Ltd.] was placed in a glass reaction vessel equipped with a stirrer. After vacuum drying for 1 hour and then purging with nitrogen, 750 ml of chloroform was added and stirred at 35 ° C. for 2 hours to dissolve. After dissolution, 160 ml of chloromethyl ethyl ether and 6.74 ml of tin chloride were added and stirred at 35 ° C. for 8 hours. Next, the reaction solution was added to 4 L of methanol, and the precipitate was washed and dried to obtain chloromethylated SEBS. The chloromethylation rate of chloromethylated SEBS was 55.1 mol% of styrene units from ¹ H-NMR analysis.
Next, a SEBS film having a quaternary ammonium hydroxide group was obtained by amination and ion exchange in the same manner as in Example 1 (1). The film thickness was 100 μm, and the ion exchange capacity was 1.31 meq / g in terms of the value obtained by ¹ H-NMR measurement.

Performance Test of Polymer Membranes of Examples and Comparative Examples as Ion Conductive Binders for Solid Polymer Fuel Cells Examples 1 (1), 2 (1) and Comparative Examples in the tests 1) and 2) below The block copolymer film having a quaternary ammonium hydroxide group obtained in 1 was used as a sample.
1) Measurement of hydroxide ion conductivity A sample of 1 cm × 4 cm was sandwiched between a pair of platinum electrodes and attached to an open cell. The measurement cell was installed in a constant temperature and humidity chamber adjusted to a temperature of 60 ° C. and a relative humidity of 90%, and hydroxide ion conductivity was measured by an AC impedance method.
2) Oxidation stability test A sample was added to a 3 mass% hydrogen peroxide aqueous solution set at 60 ° C and allowed to react for 5 hours and 10 hours. Next, after immersing the sample in 0.5N NaOH for 1 hour, the sample was sufficiently washed with distilled water, dried, and subjected to weight measurement and ion conductivity measurement.
3) Fuel cell single cell output performance evaluation About the polymer electrolyte fuel cell single cell produced in Example 1 (2) and Example 2 (2), the fuel cell output performance was evaluated. Humidified hydrogen was used as the fuel, and humidified oxygen was used as the oxidant. The test was conducted at a cell temperature of 80 ° C. under conditions of hydrogen: 500 cc / min and oxygen: 500 cc / min.

As a result of the performance test as an ion conductive binder, the block copolymer having a quaternary ammonium hydroxide group produced in Example 1 (1), Example 2 (1), and Comparative Example 1 was subjected to hydroxide ion conduction. Table 1 shows the results of the measurement of the degree and the oxidation stability test. Comparison of Example 1 and Example 2 in Table 1 revealed that the hydroxide ion conductivity was improved with an increase in the introduction rate of quaternary ammonium hydroxide groups. From a comparison between Example 1 and Comparative Example 1, it was clarified that the same level of hydroxide ion conductivity was exhibited even if the polymer skeleton was different.
In addition, from the results in Table 1, the quaternary ammonium type anion exchange type electrolyte comprising the α-methylstyrene block copolymer of the present invention is quaternary ammonium having a mass retention rate of SEBS in the oxidation stability test. It was found to be significantly higher than the type of anion exchange electrolyte.

As the power generation characteristics of the polymer electrolyte fuel cell single cells produced in Example 1 (2) and Example 2 (2), a change in voltage with respect to current density was measured. The results are shown in FIGS.
Open-circuit voltage of the single cells together about 1.0 V, the maximum power density in Example 1, 145 mW / cm ^2, a second embodiment the 38 mW / cm ^2, the ion-conducting binder of the present invention is a polymer electrolyte fuel cell It became clear that it could be used for

It is a figure which shows the current density-output voltage of the single cell for polymer electrolyte fuel cells (Example 1 (2)). It is a figure which shows the current density-output voltage of the single cell for polymer electrolyte fuel cells (Example 2 (2)).

Claims (14)

An ion conductive binder used for a membrane-electrode assembly for a polymer electrolyte fuel cell, comprising a polymer electrolyte membrane and two gas diffusion electrodes joined to the polymer electrolyte membrane with the membrane interposed therebetween. A block copolymer containing a polymer block (A) having an aromatic vinyl compound unit whose α-carbon is a quaternary carbon as a main repeating unit and a flexible polymer block (B) as constituent components And the polymer block (A) has a monovalent anion conductive group, or the polyvalent anion conductive group is bonded in a form of cross-linking the polymer blocks (A), and / or The ion conductive binder in which a polyvalent anion conductive group is bonded in a form of cross-linking aromatic vinyl compound units in the polymer block (A). The ion conductive binder according to claim 1, wherein the proportion of the aromatic vinyl compound unit in which the α-carbon in the polymer block (A) is quaternary carbon is 50% by mass or more. The ion conductive binder according to claim 1 or 2, wherein the mass ratio of the polymer block (A) to the polymer block (B) is 95: 5 to 5:95. In the aromatic vinyl compound unit in which the α-carbon is a quaternary carbon, the hydrogen atom bonded to the α-carbon atom is an alkyl group having 1 to 4 carbon atoms, a halogenated alkyl group having 1 to 4 carbon atoms, or a phenyl group. The ion conductive binder according to any one of claims 1 to 3, which is a substituted aromatic vinyl compound unit. The flexible polymer block (B) is an alkene unit having 2 to 8 carbon atoms, a cycloalkene unit having 5 to 8 carbon atoms, a vinylcycloalkene unit having 7 to 10 carbon atoms, a conjugated diene unit having 4 to 8 carbon atoms, and carbon. A conjugated cycloalkadiene unit having 5 to 8 carbon atoms, a vinylcycloalkene unit having 7 to 10 carbon atoms in which part or all of the carbon-carbon double bond has been hydrogenated, a conjugated diene unit having 4 to 8 carbon atoms and carbon The ion conductive binder according to any one of claims 1 to 4, which is a polymer block composed of at least one repeating unit selected from the group consisting of conjugated cycloalkadiene units of formula 5-8. The flexible polymer block (B) is an alkene unit having 2 to 8 carbon atoms, a conjugated diene unit having 4 to 8 carbon atoms, and 4 to 8 carbon atoms in which some or all of the carbon-carbon double bonds are hydrogenated. The ion conductive binder according to any one of claims 1 to 4, which is a polymer block comprising at least one repeating unit selected from conjugated diene units. The aromatic vinyl compound unit in which the α-carbon is a quaternary carbon is an α-methylstyrene unit, and the flexible polymer block (B) is a conjugated diene unit having 4 to 8 carbon atoms and one carbon-carbon double bond. The ion-conductive binder according to any one of claims 1 to 4, which is at least one repeating unit selected from conjugated diene units having 4 to 8 carbon atoms, all or part of which are hydrogenated. The ion conductive binder according to any one of claims 1 to 7, wherein the anion conductive group is at least one selected from the following groups (1) to (13).

(In the above formula, R ^{1 to} R ³ each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ^{4 to} R ⁹ and R ¹¹ each independently represents a hydrogen atom, a methyl group or an ethyl group. , R ¹⁰ represents a methyl group or an ethyl group, X ⁻ represents a hydroxide ion or an acid anion, m represents an integer of 2 to 6, and n represents 2 or 3. The ion conductive binder according to claim 8, wherein R ^{1 to} R ⁹ and R ¹¹ are a methyl group or an ethyl group, and X ^- is a hydroxide ion. The ion-conductive binder according to claim 9, wherein R ^{1 to} R ¹¹ are methyl groups. The ion-conductive binder according to any one of claims 1 to 10, wherein the block copolymer has an ion exchange capacity of 0.30 meq / g or more. The solution or suspension containing the ion conductive binder of any one of Claims 1-11. The membrane-electrode assembly using the ion-conductive binder of any one of Claims 1-11. A polymer electrolyte fuel cell using the membrane-electrode assembly according to claim 13.

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